Beau Biden's Stroke Shows Younger Adults Also at Risk

Doctors treating Beau Biden, the 41-year-old son of Joe Biden, and Delaware's attorney general, have not yet revealed the underlying cause or the nature of the "mild stroke" that he experienced on Tuesday, but neurologists said that such strokes can arise from any of a number of underlying factors.

Dr. Timothy Gardner, medical director of the Center for Heart and Vascular Surgery at Christiana Care Health System and the doctor who treated Biden, said he likely will have a full recovery.

"[He is] fully alert, in stable condition and has full motor and speech skills," Gardner said in a statement.

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Hospital officials said Biden was communicating with his wife and parents, who were with him. On Tuesday evening he was transferred to Thomas Jefferson University Hospital in Philadelphia for "further observation and examination," according to the vice president's office.

Biden's doctors have not yet revealed whether his stroke was hemorrhagic (due to a blood vessel bursting in his brain) or ischemic (brought about by a clot that blocked the blood supply to part of his brain). The distinction is important, as treatments for the two kinds of stroke differ greatly.

Still, some doctors say that even when more details are available, the exact cause of a stroke can be difficult to pinpoint.

ABC News senior health and medical editor Dr. Richard Besser spoke with Dr. Anthony Furlan, co-director of the Neurological Institute at Case Western Reserve University in Cleveland, Ohio. Furlan said that, indeed, in most cases of stroke in patients younger than 50, the exact cause remains a mystery.

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"Often after a stroke, they will find a [heart-related cause] that was undetected," Furlan said.

One such heart problem is known as patent foramen ovale -- a small hole in the heart that allows clots to pass from one side of the heart to the other. Sometimes these clots can enter the brain and bring on a stroke.

Biden's Stroke Not Likely Related to Father's Aneurysm

Then there is the fact Joe Biden had two separate surgeries in 1988 to repair brain aneurysms, a bulging of the blood vessel that can lead to hemorrhagic stroke. However, doctors were quick to point out that this does not necessarily mean the vice president's son has the same ailment.

"If there were a strong suspicion that this was an aneurysm, it's unlikely the institution would label it a stroke," said Dr. Steven Gianotta, chairman of the department of neurological surgery at the USC Keck School of Medicine in Los Angeles.

"Despite a father with an aneurysm, the most likely cause of a stroke in a young person like this would be a dissection of either the carotid or vertebral artery," he said. "This is a spontaneous tear in the inner lining of the artery that can cause a partial or total blockage, or shower blood clots up to the brain."

Furlan, too, said that it is unlikely that the stroke had to do with an aneurysm.

"Based on the press reports, [there was] no evidence of bleeding," he said, adding that the stroke is "probably unrelated to his father's aneurysm."

Possible causes, Furlan said, would be high blood pressure, diabetes, high cholesterol or smoking status, all of which could lead to the artery-hardening condition atherosclerosis, which in turn makes stroke more likely.